1. Field of the Invention
The present invention relates to a photoelectric converting film stack type solid-state image pickup device in which a photoelectric converting film that generates charges corresponding to the amount of received light is stacked on a semiconductor substrate, and more particularly to a photoelectric converting film stack type solid-state image pickup device in which a signal charge generated in a photoelectric converting film is transferred through a charge transfer path on a semiconductor substrate to be read out to the outside.
2. Description of the Related Art
In a CCD solid-state image pickup device or a CMOS solid-state image pickup device which is mounted on a digital camera, a large number of photoelectric converting elements (photodiodes) serving as light receiving portions, and signal read circuits which read out photoelectric conversion signals obtained in the photoelectric converting elements are formed on the surface of a semiconductor substrate. The signal read circuits are configured by, in the case of a CCD device, charge transfer circuits and transfer electrodes, or by, in the case of a CMOS device, MOS transistor circuits and signal lines.
In the related-art solid-state image pickup device, therefore, many light receiving portions and signal read circuits must be formed on the same surface of a semiconductor substrate, thereby producing a problem in that the area for the light receiving portions cannot be increased.
The related-art single-type solid-state image pickup device has a configuration in which one of color filters of, for example, red (R), green (G), and blue (B) is stacked on each of light receiving portions, so that the light receiving portion detects a light signal of the one color. In the position of a light receiving portion which detects light of, for example, red, therefore, blue and green signals are obtained by interpolating detection signals of surrounding light receiving portions which detect blue light and green light, respectively. This causes a false color, and reduces the resolution. Furthermore, blue light and green light incident on a light receiving portion where a red color filter is formed do not contribute to photoelectric conversion, but are absorbed as heat into the color filter, thereby producing another problem in that the light use efficiency is poor and the sensitivity is low.
As described above, the related-art solid-state image pickup device has various problems. On the other hand, in such a device, the number of pixels is advancing. At present, a large number or several millions of pixels or light receiving portions are integrated on one chip of a semiconductor substrate, and the size of an opening of each of the light receiving portions is near the order of the wavelength. Consequently, a CCD device and a CMOS device are hardly expected to configure an image sensor which can solve the above-discussed problems, and which is superior in image quality and sensitivity than the related-art one.
Therefore, attention is again paid to the structure of a solid-state image pickup device which is disclosed in, for example, JP-A-58-103165. The solid-state image pickup device has a structure where a red-detection photosensitive layer, a green-detection photosensitive layer, and a blue-detection photosensitive layer are stacked by a film growth technique on a semiconductor substrate in which signal read circuits are formed on the surface, these photosensitive layers are used as light receiving portions, and photoelectric conversion signals obtained in the photosensitive layers are supplied to the outside by the signal read circuits. Namely, the solid-state image pickup device has a structure of a photoelectric converting film stack type.
In this structure, it is not required to dispose the light receiving portions on the surface of the semiconductor substrate. Therefore, restrictions on the design of the signal read circuits are largely eliminated, and the light use efficiency of incident light is improved, so that the sensitivity is enhanced. Moreover, one pixel can detect light of the three primary colors or red, green, and blue. Therefore, the resolution is improved, and a false color does not occur. As a result, it is possible to solve the above-discussed problems of the related-art CCD or CMOS solid-state image pickup device.
Recently, photoelectric converting film stack type solid-state image pickup devices disclosed in JP-A-2002-83946, JP-T-2002-502120, JP-T-2003-502847 and Japanese Patent No. 3,405,099 have been proposed. An organic semiconductor or nanoparticles are used as the photosensitive layers.
In a photoelectric converting film stack type solid-state image pickup device in which a signal read circuit is configured by charge transfer paths, photo-charges generated in photoelectric converting films stacked on a semiconductor substrate must be read out to the charge transfer paths to be transferred. FIG. 6 is a surface diagram of vertical transfer paths in a photoelectric converting film stack type solid-state image pickup device disclosed in, for example, JP-A-2002-83946.
The photoelectric converting film stack type solid-state image pickup device has a configuration where one pixel 10 indicated by the broken-line rectangular frame reads out and transfers photo-charges of three colors or red, green, and blue. In the device, therefore, three vertical transfer paths (vertical CCD registers configured by an n-type semiconductor) 11r, 11g, 11b corresponding to pixels arranged in the row (horizontal) direction are separated by channel stops (p+ regions) 12.
At the same vertical position (first-phase transfer electrode) Φv1 of the vertical transfer paths 11r, 11g, 11b, charge accumulating portions 13r, 13g, 13b are defined by the channel stops 12 which are formed into a U-like shape. Longitudinal lines upstand at contact portions 14r, 14g, 14b configured by an n+ region which are disposed at the middles of the charge accumulating portions 13r, 13g, 13b, and are connected to the upper layers or the photoelectric converting films for the respective colors. Signal read gate regions 15r, 15g, 15b are disposed at the sides (the open end sides of the U-like shapes) of the charge accumulating portions 13r, 13g, 13b. 
Subsequent to the first-phase transfer electrode Φv1, a second-phase transfer electrode Φv2, a third-phase transfer electrode Φv3, and a fourth-phase transfer electrode Φv4 are sequentially disposed in the vertical direction of the vertical transfer paths 11r, 11g, 11b. In the next first-phase transfer electrode Φv1, charge accumulating portions (not shown) are disposed in the same manner as described above.
Red signal charges generated in the upper layer or the red photoelectric converting film are accumulated in the charge accumulating portion 13r, green signal charges generated in the green photoelectric converting film are accumulated in the charge accumulating portion 13g, and blue signal charges generated in the blue photoelectric converting film are accumulated in the charge accumulating portion 13b. The charges accumulated in the charge accumulating portions 13r, 13g, 13b are read out through the read gate regions 15r, 15g, 15b to the vertical transfer paths 11r, 11g, 11b, and then transferred in the vertical direction by the four-phase drive.
In the photoelectric converting film stack type solid-state image pickup device having the vertical transfer paths shown in FIG. 6, the charge accumulating portions 13r, 13g, 13b for the respective colors are aligned in line at the same vertical position. In the vertical transfer paths 11r, 11g, 11b, therefore, the widths of the vertical transfer paths below the first-phase transfer electrode Φv1 are narrowed, and there arises a trouble that the transfer efficiency is reduced by the narrow-channel effect. As a result, the pixel pitch in the row (horizontal) direction cannot be reduced, and a photoelectric converting film stack type solid-state image pickup device of a high resolution cannot be realized.
The upper limit of the quantity of charges transferred by the vertical transfer paths 11r, 11g, 11b driven by the four-phase drive is determined by a portion where the sum of the areas of two transfer electrodes adjacent in the vertical direction is smallest. In the configuration of FIG. 6, namely, the maximum quantity of transferred charges is determined by the sum of the areas of the second-phase transfer electrode Φv2 or the fourth-phase transfer electrode Φv4, and the first-phase transfer electrode Φv1 having an area which is extremely small. Therefore, the configuration of FIG. 6 has a problem in that the maximum quantity of transferred charges is largely restricted by the first-phase transfer electrode Φv1 and the saturation power is reduced. It is difficult to realize a photoelectric converting film stack type solid-state image pickup device having a wide dynamic range.